Intramolecular aldol condensation reactions and transacetalization equilibria

摘要

Part I. Intramolecular aldol condensation reactions. The detailed kinetics and equilibrium for the intramolecular aldol condensation reaction of 2,5-hexanedione, 2, 6-heptanedione, 1-phenyl-1, 5-hexanedione and 5-oxohexanal were studied and correlated in terms of Marcus theory. All the reactions, with the readily explained exception of the intramolecular aldol addition of 5-oxohexanal, gave us approximately constant intrinsic barriers: 14.49 $pm$ 0.82 kcal/mol for the intramolecular aldol addition step and 13.99 $pm$ 0.74 kcal/mol for the subsequent dehydration step, which are also in excellent agreement with the intrinsic barriers found for intermolecular aldol condensation reactions.$sp{16}$ This means that Marcus theory is applicable to intramolecular aldol condensation reactions. With an equilibrium constant estimated in some way, we can now predict the rate constant for an intramolecular aldol condensation reaction based on the results of this work!;Part II. Equilibrium constant determination for acetal formation reactions. Three transacetalization equilibria were measured directly in methanol by $sp1$H-NMR. This constructed a ladder of equilibrium constants from acetophenone, for which the equilibrium constant for acetal formation has been measured, to methyl formate, for which it has not. This is the first direct measurement of an equilibrium constant for formation of an acetal of an acyclic ester.